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Ogive - The curved portion of a bullet ahead of the cylindrical, or shank, section. Also, the radius of this curve, usually expressed in calibers.

Oil Dent - Dent in a cartridge case formed by too much oil or lubricant when sizing. Usually seen on the shoulder of bottleneck cases.

Overbore Capacity - A common but unscientific term referring to a cartridge case that has too much case volume for its bore volume. Technically, every case can be over its bore capacity with some powder. Generally used when a case has a volume so large in relation to the bore diameter that only the very slow burning powders will give satisfactory performance, or very little velocity is gained by adding more powder.